Influence of topographically driven convection on heat flow in the Swiss Alps: a model study

Abstract

A 2-D thermohydraulic model for two sites in Switzerland is presented. Geologically both sites belong to Alpine nappe units and consist of generally low permeable rocks with hydraulic conductivities in the range of 10 −10–10 −8 m s −1. Elevation of topography attains 2.4–3.1 km, and the mountain water table exhibits a correspondingly high relief. The geothermal regime of the area is characterized by relatively high values of measured heat flow on the order of 80–100 mW m −2. The results reveal well developed subsurface fluid circulation systems in both cases. The vertical fluid velocities reach some cm/yr, which is higher by more than one order of magnitude than the flow rates in flat terrain. In mountainous terrain, flow systems may penetrate to depths of 2–3 km below sea level. The discharge zones in areas with high relief and steep slopes are rather narrow and concentrate at and near the valley bottoms. Such zones are the regions of heating where positive disturbances may reach up to 1.5–1.8 times the basal heat flow value. In the recharge areas at ridges, heat flow may in turn become quite low. The calculated thermohydraulic models have been validated by measured temperature distributions in drillholes. Reasonably good agreement between the measured and the calculated temperatures exists for both sites.